A number of different machines are currently available for use in the curing of rubber tires during tire manufacturing processes. Examples of such machinery are those described in New Zealand Patent Specification Nos. 168572 and 168660. In these processes a reusable rubber or the like curing bag or bladder is during curing cycles inflated to force outward a green tire into parts of the tire mould. Normally each bag or bladder can be reused up to 200 times before it deteriorates under the pressures and temperatures involved in the curing process.
Deterioration of the bag or bladder, which is usually referred to as reversion, normally occurs because of oxidation due to oxygen being trapped in the bag or bladder as it is inflated. Over the years attempts have been made to reduce the rate at which reversion takes place and thus lengthen the reusable life of the bag or bladder. For example it is recognised that the use of an inert gas for pre-shaping of the bag or bladder within a green tire or purging of curing and/or cooling medium from the bag or bladder at completion of curing is advantageous because the insert gas acts as a preservative by preventing oxidation. For example in U.S. Pat. Nos. 4,126,657 and 4,222,721 the use of an inert gas for purging is disclosed while in European Patent Specification Nos. 0052522 and Australian Patent Specification No. 18261 an inert gas is disclosed as being used for pre-shaping purposes.
Despite these attempts at reducing the rate at which reversion occurs the effective reusable life of a bag or bladder has remained a problem as reversion has continued to take place at an unacceptable level. It is evident that even when an inert gas or indeed other non-reactive medium is employed for pre-shaping and/or purging, oxygen still becomes trapped in the bag or bladder. The main object of the present invention is thus to provide a tire manufacturing process in which the wear life of a curing bag or bladder is increased by reducing the rate at which reversion occurs due to oxygen being trapped in the bag or bladder.